Gutless 401 ?

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Triumph215
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Gutless 401 ?

Post by Triumph215 »

How powerful is your 401? How fast do you normally drive on the highway? I know it's a '77 but it still seems pretty underpowered to me but this is my first 401 so I wanted to ask.
When I bought this in January I just figured it was in poor shape which was true but now it should be running pretty well. I've repaired/replaced damn near everything. Electronic ignition conversion, timing at 12-13 degrees static, electrical system/battery all grounded properly with new cables. No vacuum leaks, new 1978 distributor with new cap, rotor and wires. I'm using manifold vacuum.
I have not disassembled the carb, it's a reman Motorcraft 4350, plugs looked fine and are gapped at .040 or so so I left them in. I haven't done a compression test but all the plugs looked the same and the engine doesn't smoke at all.
I replaced the carb base gaskets this weekend out of abundance of caution and the back of the thick top gasket was really wet but I'm driving it daily so maybe that's normal.
I looked up my Infinity and it weighs 4,200lbs and has 267 Nm of torque, the Wag should have 413 Nm and weighs 4,370 lbs. The Infiniti would walk the dog on the Wag off the line and in passing power so I suspect I'm not doing something right.
I was really thinking it would have more balls for a large displacement engine, there's no way I'd try to tow anything with it.
Is something wrong or is this normal?
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Renodemona
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Re: Gutless 401 ?

Post by Renodemona »

I dunno, mine does fine. It's no race car. Its rated at 225 hp but 325 torques. What gears do you have? Are you running stock style, but new distributor? Going to a HEI or TFI (I think? I dunno the ford big cap thing) does wonders for snap and acceleration. I tow a horse trailer every once in a while, it does fine. Tent trailer it didn't notice at all.

On the highway I try and keep it under 70 but I've perhaps maybe unconfirmed 80 once or twice...
"Wait, what's on fire!?" KJ7TCT
--------------------------------------------------------------
1976 Cherokee w/t 'Susan' 401/TH400/QT(PT)
FiTech Go EFI, Edelbrock Performer intake
3" Rough Country Springs, HEI Dizzy
-------------------------------------------------------------
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Stuka
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Re: Gutless 401 ?

Post by Stuka »

Have you done a compression check or anything on it? Low compression would definitely make it feel slow.

Do you have larger than stock tires? Larger tires raise your gear ratio, essentially making it slower.

The 4350 is not a great carb, but its not terrible provided its working correctly.

I cannot recall if '77 had a cat, but if it does, are you sure it isn't plugged?
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Triumph215
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Re: Gutless 401 ?

Post by Triumph215 »

Since I'm new to the engine and it was previously neglected I'm still a little hesitant to keep up with traffic on the highway. Going over 70 spins it pretty hard, not sure how fine that is for these engines. Thanks for the feedback.
Plugged exhaust is where my current thinking lies but I have no idea how to check for that.
I don't think I can replace that carb due to Smog laws but always had good luck getting Q-jets to work so I don't hate the carb yet. I might have to open it up to check the reman but they've glued it shut or something and i couldn't get it apart easily so I just put it back on and crossed my fingers.
I did do the stealth ignition conversion with the big ugly cap,
The PO did put big tires on it and I haven't confirmed my gear ratio, I've been wondering about that anyway. ll get those numbers together.
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tgreese
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Re: Gutless 401 ?

Post by tgreese »

When you say "spins pretty hard" do you mean loud? It's a Jeep, and I would expect lots of engine noise on the highway, especially if the interior padding and carpet has been removed.

Supposedly you can test for a plugged cat with a vacuum guage. Several available on Amazon for cheap. Also the plugged cat will get hot? Easy to test with an infrared laser thermometer. I would expect the TSM has something about this.

Again, the TSM lists the available ratios. Most likely you have the standard one... 3.31? Looking. Oooh, 3.07s standard, 3.54 optional. 3.07s are highway gears, and a shorter tire would help.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
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Stuka
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Re: Gutless 401 ?

Post by Stuka »

Triumph215 wrote: Thu May 13, 2021 7:53 am Since I'm new to the engine and it was previously neglected I'm still a little hesitant to keep up with traffic on the highway. Going over 70 spins it pretty hard, not sure how fine that is for these engines. Thanks for the feedback.
Plugged exhaust is where my current thinking lies but I have no idea how to check for that.
I don't think I can replace that carb due to Smog laws but always had good luck getting Q-jets to work so I don't hate the carb yet. I might have to open it up to check the reman but they've glued it shut or something and i couldn't get it apart easily so I just put it back on and crossed my fingers.
I did do the stealth ignition conversion with the big ugly cap,
The PO did put big tires on it and I haven't confirmed my gear ratio, I've been wondering about that anyway. ll get those numbers together.
So if you have larger sized tires with stock gears, your speedometer will be wrong. It very well may say 70, and you will actually be doing 80.

Spinning more RPM is because you don't have overdrive like modern vehicles do. So you will run more RPM. That wont make your acceleration slower, just makes you run more RPM on the HWY.

The 4350 isn't a quadra-jet. It is a spread bore, but is a different design that was developed for Fords. If you ever choose to ditch the carb, there are smog legal EFI solutions, and a few (like two) smog legal Carbs you could go with.
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Triumph215
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Re: Gutless 401 ?

Post by Triumph215 »

RPM's are higher than I'd like understanding there are only three gears, the tires aren't THAT big but shorter tires are a good idea. :) Speedo says 65 and I'm the slowest thing on the highway plus I went through a few automated radar signs lately and my speedo is slightly optimistic.
I have the original build sheet, I wonder if it's on there ?
In the meantime I'm going to plumb my vacuum gauge into the cab and go for a drive to see if that Cat is plugged. I'm also planning to buy one of those infrared thermometers, I've been wanting one for awhile anyway. It's pretty peppy in town but on the highway it'll barely get out of it's own way. AND rpm's are high. I'm going to search for a power curve chart too.
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Renodemona
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Re: Gutless 401 ?

Post by Renodemona »

What size tires do you have? What RPMs are you pulling? You should be able to see your gear ratio on the build sheet or if you are lucky the tag is on the axle. If you have the tow package you will have 3.54 (that's what I have). I think 3.31 or 3.07 are the other options. 3.31 is ok. 3.07 is not optimal, especially if you have 33s. Your speedo is kind of a best guess gauge even if its aligned with the correct gear ratio.

Throw a youtube video up, sometimes how it sounds helps.
"Wait, what's on fire!?" KJ7TCT
--------------------------------------------------------------
1976 Cherokee w/t 'Susan' 401/TH400/QT(PT)
FiTech Go EFI, Edelbrock Performer intake
3" Rough Country Springs, HEI Dizzy
-------------------------------------------------------------
2018 Cherokee Trailhawk V6 'Sedna'

rocklaurence
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Re: Gutless 401 ?

Post by rocklaurence »

Something isnt right. You could take it to a Speed shop for them to figure out. Tony/Lucky [Motor Trend] did a story on a AMC 401 with cam and new heads and it ran 400+HP.
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Re: Gutless 401 ?

Post by tgreese »

Triumph215 wrote: Thu May 13, 2021 9:12 pm RPM's are higher than I'd like understanding there are only three gears, the tires aren't THAT big but shorter tires are a good idea. ...
It would be easier to help you if you would supply more numbers in your reply. "RPMs are higher" does not mean much without numbers. Your impressions aren't worth very much as evidence. Measure. Measure, measure, measure.

Suggest you get a GPS or use your cell phone as a GPS and get an accurate idea of how fast you are going. You can do this with a measured mile and stopwatch too, if there is one posted on a highway near you.

You need to do a compression check. A compression tester is cheap at Harbor Freight or on Amazon. Measure the vacuum at idle and at highway speed. Both the vacuum gauge and the compression gauge will come with instructions. Measure.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
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letank
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Re: Gutless 401 ?

Post by letank »

X2 as said above. As for my test drive of a rebuilt 401, over 10 years ago... beside the impressive receipts of $10K, and single digit mpg, it was gutless, I told the seller to tweak the timing a tad...
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Triumph215
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Re: Gutless 401 ?

Post by Triumph215 »

Axles are 3.54, tires are 29.5" tall, speedometer appears pretty close according to radar speed signs along the road.
An rpm calculator on the web says if my speedo is correct then I'm turning almost 2,900 at 70 and about 2,600 at 65.
I checked my Cat with an IR Temp gun and it's 100 degrees cooler at the front than at the rear so that's encouraging. I still need to go fetch 6' of vacuum line so I can plumb my vacuum gauge into the cab and get out onto the highway.
It's so unpowerful on the highway which should be in the meat of the torque curve. I wish I knew someone around me with a 401 so they could drive my truck.
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Re: Gutless 401 ?

Post by Stuka »

Triumph215 wrote: Thu May 20, 2021 8:12 am Axles are 3.54, tires are 29.5" tall, speedometer appears pretty close according to radar speed signs along the road.
An rpm calculator on the web says if my speedo is correct then I'm turning almost 2,900 at 70 and about 2,600 at 65.
I checked my Cat with an IR Temp gun and it's 100 degrees cooler at the front than at the rear so that's encouraging. I still need to go fetch 6' of vacuum line so I can plumb my vacuum gauge into the cab and get out onto the highway.
It's so unpowerful on the highway which should be in the meat of the torque curve. I wish I knew someone around me with a 401 so they could drive my truck.
There isnt much of a difference between a 360 and a 401 on the HWY, so you don't have to find somebody with a 401.

I still think a compression check would be good to determine the health of the engine from a wear perspective. If compression is low, power will be too.

Its also possible the carb or timing are not set optimally. Especially if the timing we set to pass emissions, that can really hurt power in that RPM range.
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Re: Gutless 401 ?

Post by Triumph215 »

Agree about compression and I own a gauge, I just have to set the time aside and do it. Mostly I haven't because there's nothing I can do about it, that's a deeper hole than I want to step into. The PO provided a paper that shows he measured all 8 cylinders with readings of 130 for every cylinder but I don't trust those at all.
The timing is set at 13 degrees now but and I've moved it around and even to the point where it pings under load and there's little difference.
Being I just changed out the base gaskets and the thick gasket was soaking wet with gas in the back between the secondaries I'm suspicious of the reman rebuild but I want to check vacuum on the highway before I pull it apart. I tried opening it up already and they must have used adhesive on the gaskets because it refuses to come apart, that job's going to take a concentrated effort and patience. I ordered the Motorcraft 4350 Manual from the Carburetor Doctor website today and I'm hoping there will be a troubleshooting section in it.
I have the distributor connected to manifold vacuum.
The plugs are all very uniformly colored and all show a lean-ish condition, have been thinking about going to a cooler plug.
Will report back with manifold vacuum at highway speeds on Saturday.
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Re: Gutless 401 ?

Post by Stuka »

The 4350 is probably my least favorite carb rebuild that I have ever done. The manual will be nice to have for it.

If you are lean at cruise, and assuming you have no vacuum leaks, it most likely mean you need a jet change. But I am not sure if you can still get jets for a 4350.

You could get an adapter and put an Edelbrock 1400 on it, which is CARB legal 4v carburetor.
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Re: Gutless 401 ?

Post by Triumph215 »

I had to get on the highway for an hour so i hooked up the vacuum gauge.
Warm but after sitting for an hour, idle vacuum is 16lbs
10 minutes to the highway, I get on and vacuum is 13-14lbs at 65mph, flat ground, even throttle.
5 minutes later I'm at 10-11lbs
Slight inclines drop it to 7lbs
Decent incline approaching offramp and the truck won't hold 65, vacuum at 3lbs.
At home in Park, vacuum is now 18lbs
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Re: Gutless 401 ?

Post by Stuka »

Vacuum will be highest at low throttle, and lowest at WOT. If the secondaries are open, it is normal for vacuum to drop.

18-22 at sea level is what you should see for idle. If you get a chance, with the gauge hooked up, and in park, rev the engine to around 2500rpm (guess if you dont have a tach), and hold it there for about 15 second. The vacuum should stay steady for the entire time. When you let off, it should jump up to 18-22 almost instantly. If it slowly starts dropping over that time, or it doesnt bounce right back to 18, you have some sort of exhaust restriction. I know your temp gauge didn't show anything, but its worth double checking.

13-14 cruising is pretty much spot on to what you should be seeing.

3" would suggest you are at WOT, although at perhaps a lower RPM than you should be at. Did it downshift to 2nd during that hill climb? I am also not sure what is normal for a 4350 at WOT. Its possible 3 is lower than it should be, and you are perhaps lean under high throttle. Maybe the secondary main jets are plugged.

The 4350 has massive secondaries, and tiny primaries. The secondaries are also mechanical, which means they can be opened at any speed or load, including when they maybe should not be from a VE perspective. One of the things I really disliked about the 4350 when I had one was the primaries were often too small for any sort of hill, but soon as I dug into the secondaries, I could actually lose power, and letting up on the throttle some would result in me gaining speed. I ultimately swapped in an edelbrock intake/carb and it was a night and day difference. A square bore just has much better drivability. It also has mechanical secondaries, but the primaries are much larger so you dont need the secondaries as often.

Another quick thing to check, how is the fuel filter? A partially plugged one can starve the engine for fuel under high demand scenarios, but cruise and idle just fine.
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Re: Gutless 401 ?

Post by Triumph215 »

Muffler and Cat A-ok, no need to replace them.
On to the carb but it's glued together or at least I've never seen one that refused to come apart like this one has, this is going to take some patience.
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Re: Gutless 401 ?

Post by Stuka »

The 4350 has some hidden screws too, its not a fun carb to take apart, at all.
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Re: Gutless 401 ?

Post by Triumph215 »

So interesting. The rebuild went well, the carb looked great inside and I went with the larger metering rods and reset them/new gaskets and reassembled. Started right up but haven't driven yet.
Before I reinstalled the carb I checked my timing mark and the piston is at TDC 5 degrees before the zero mark so I know my valve timing is off slightly. I didn't have someone to help me so i didn't have a chance to measure timing chain slash but that's easy so will check later. My timing is at 15 degrees so will set it back a little to 12ish. Am working on the headliner today but hope to finish up early so I can get out to drive the truck.
1964 Triumph TR4 with 1964 Olds 215 heart transplant
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